1. Field of the Invention
This invention relates to moldboard plow supports and more particularly to a support which trips when an obstruction or excessive resistance to movement of the blade is encountered in order to avoid damage to the plow structure.
2. Description of the Related Art
Various kinds of plow trips have been used heretofore. One type has employed a toggle linkage and a heavy spring which biases the toggle toward the closed operating position. Such arrangements employ a spring viewed as sufficiently strong to return the plow to its operating position as soon as the obstruction is passed. An example is shown in the patents to Simpson 2,565,668, Ralston et al. 3,976,144, and Good 4,609,051 (spring plus gravity return). Another type has the links in an off-center relationship so that when an obstruction is encountered the center linkage passes through dead center. A spring is provided to tend to urge the links in the off-center relationship. An example of such patents is Johnson et al. 3,910,354 and Crosby 4,312,407.
The patent to Bergerson 2,863,372, discloses a spring biased detent which engages a slide member and normally holds the plow in plowing position but which permits it to lift to the rear when an obstruction is encountered.
Green et al. 4,128,130, discloses a biased four bar linkage which permits the tool to pass over obstacles that are encountered but which restores the tool to earth penetrating position after it has been tripped.
The patent to Venable et al. 3,972,374, discloses a linkage mechanism including a spring biased linkage mechanism and a pivot riding in an enlarged opening tending to hold the links extended, the arrangement permitting tripping of the plow after which the operator raises the main frame in order to permit the weight of the apparatus to return the linkage to normal position.